The present invention relates generally to planarizing a surface of a semiconductor wafer, and more particularly to an apparatus and method for linearly planarizing a surface of a semiconductor wafer with a belt.
The available systems for the chemical mechanical planarization (CMP) of semiconductor wafers typically employ a rotating wafer holder for supporting the wafer and a polishing pad which is rotated relative to the wafer surface. The wafer holder presses the wafer surface against the polishing pad during the planarization process and rotates the wafer about an axis relative to the polishing pad. The polishing pad is carried by a polishing wheel or platen which is rotated about a another axis different from the rotational axis of the wafer holder. A polishing agent or slurry is applied to the polishing pad to chemically enhance the polishing of the wafer. As the wafer holder and the polishing wheel are each rotated about their respective central axes, an arm moves the wafer holder in a direction parallel to the surface of the polishing wheel.
Since the polishing rate applied to the wafer surface is proportional to the relative velocity of the polishing pad, the polishing rate at a selected point on the wafer surface depends upon the distance of the selected point from the axis of rotation. Thus, the polishing rate applied to the edge of the wafer closest to the rotational axis of the polishing pad is less than the polishing rate applied to the opposite edge of the wafer. Rotating the wafer throughout the planarization process averages the polishing rate applied across the wafer surface so that a uniform average polishing rate is applied to the wafer surface. Although the average polishing rate may be uniform, the wafer surface is continuously exposed to a variable polishing rate during the planarization process. In addition, fluid dynamic and thermodynamic factors effect the chemical reactions occurring during the planarization process and can influence the actual polishing rate at any given instant in time. The aforementioned effects are not uniform across the wafer surface, and thus can have a detrimental effect on the planarization process. Moreover, instead of xe2x80x9caveragingxe2x80x9d the effects, the relative rotation of the wafer and the polishing pad contribute to the fluid dynamics and thermodynamics of the chemical reaction taking place on the wafer surface and can thus further decrease the uniformity of the polishing rate.
One technique for obtaining a more uniform polishing rate is to utilize a linear polisher. Instead of a rotating pad, a moving belt is used to linearly move the pad across the wafer surface. The wafer is still rotated for averaging out the local variations, but the global planarity is improved over CMP tools using rotating pads. However, a significant problem associated with the belt utilized in linear polisher systems is that the belt is constructed from a number of individual segments which are secured adjacent to one another on a backing in such a way so as to create one or more seams in the belt. Therefore, each belt has a number of seams defined thereon which decrease the surface uniformity of the belt which can in turn adversely effect the planarization of the wafer surface. For example, slurry can accumulate and coagulate in the seams and scratch the surface of the wafer during the CMP process. The aforementioned problems cause increase the defectivity of the wafer and thus decrease the reliability of the CMP process to produce uniformly planarized. Moreover, the belts are more likely to peel at the seams which decreases the belt life and thus increases the cost of the CMP process.
Thus, a continuing need exists for a method and an apparatus for planarizing a semiconductor wafer which addresses the above described problems.
In accordance with one embodiment of the present invention, there is provided an apparatus for planarizing a surface of a semiconductor wafer. The apparatus includes a wafer support configured to receive the semiconductor wafer so that the surface of the semiconductor wafer projects from the wafer support. The apparatus also includes a polishing member configured in the form of an endless belt which is devoid of seams. The endless belt is (i) positioned in contact with the surface of the semiconductor wafer and (ii) capable of moving in a linear direction relative to the surface of the semiconductor wafer so as to planarize the surface of the semiconductor wafer.
In accordance with another embodiment of the present invention, there is provided a method of planarizing a surface of a semiconductor wafer. The method includes the steps of (i) positioning an endless belt which is devoid of seams in contact with the surface of the semiconductor wafer and (ii) moving the endless belt in a linear direction relative to the semiconductor wafer so as to planarize the surface of the semiconductor wafer.
In accordance with yet another embodiment of the present invention, there is provided an apparatus for planarizing a surface of a semiconductor wafer. The apparatus includes a wafer support configured to receive the semiconductor wafer so that the surface of the semiconductor wafer projects from the wafer support. The apparatus also includes a polishing member configured in the form of an endless unitary belt which is devoid of seams. The endless unitary belt is produced by a process which includes the steps of (i) melting a material, (ii) injecting the melted material into a cavity defined in a mold, and (iii) solidifying the melted material within the cavity so as to produce the endless unitary belt. The endless unitary belt is (i) positioned in contact with the surface of the semiconductor wafer and (ii) capable of moving in a linear direction relative to the surface of the semiconductor wafer so as to planarize the surface of the semiconductor wafer. The apparatus further includes a slurry dispensing mechanism for dispensing a chemical slurry on the endless unitary belt.
It is an object of the present invention to provide a new and useful apparatus and method for linearly planarizing a surface of a semiconductor wafer.
It is also an object of the present invention to provide an improved apparatus and method for linearly planarizing a surface of a semiconductor wafer.
It is yet another object of the present invention to provide an apparatus and method which enhances the uniformity of linearly planarizing a surface of a semiconductor wafer.
The above and other objects, features, and advantages of the present invention will become apparent from the following description and the attached drawings.